Failure analysis of high carbon steel wire rods

Failure analysis of wire rods of JIS-G-3506 (1975), SWRH-77B steel grade of the dia 13 mm was carried out. The wire rods broke during pre-drawing heat treatment (patenting) process. The wire rods were uncoiled and passed through a gas fired heating furnace for austinizing at 930C and through a molten lead bath at 550C and again coiled. The speed of the wire rods during the process remained constant i.e. 0.5 m/min and the driving force was supplied through pulling the coils only. The wire rods fractured in the molten lead bath and near the coiler for recoiling. The metallographic, chemical and mechanical analysis and fractography was carried out, and was concluded that the material of the rod was contaminated by the nonmetallic (probably slag entrapped) inclusions specially at the surface of the rod. Seam lines, deep pits and cracks were observed at the surface of the rod. Therefore, when these rods were bent on pulleys during the patenting and any/some of the weak zones come perpendicular to tensile stress a localized 'shearing' took place giving rise to crack initiation which later propagated in brittle cleavage mode to give rise to the final fracture. (author)